This section is from the book "Applied Anatomy: The Construction Of The Human Body", by Gwilym G. Davis. Also available from Amazon: Applied anatomy: The construction of the human body.
On examining a transverse section made below the foramen of Winslow, the peritoneum is seen coming from the parietes and passing over the ascending colon, leaving its posterior surface uncovered. Thence it passes over the vena cava and spine, to go to the mesentery and small intestines. Returning to the spine, it passes over the aorta, and out over the descending colon, usually leaving a portion of its posterior surface uncovered. Thence it returns to the anterior parietes.
In a section made passing through the foramen of Winslow (Fig. 413), the mode of formation of the lesser cavity of the peritoneum and the relation of the peritoneum to the stomach, spleen, and kidneys will be more readily understood. Beginning on the anterior abdominal wall, at the median line and proceeding to the right, the peritoneum is seen to enclose the round ligament of the liver, forming a mesentery for it named the falciform ligament. Continuing around, the peritoneum lines the inner surface of the anterior and lateral abdominal walls, covers the anterior surface of the right kidney, and, after forming the posterior wall of the foramen of Winslow, covers the vena cava, aorta, spine, and pancreas; it then passes over the left kidney to go to the spleen, forming the anterior layer of the lienorenal ligament. It is then reflected from the spleen to the posterior surface of the stomach, forming the posterior layer of the gastrosplenic omentum. From thence it passes forward on the stomach, past the pylorus to the upper surface of the first portion of the duodenum. Here it winds around the hepatic artery, portal vein, and common bile duct to reach the anterior surface of the stomach. This reflection forms the free anterior edge of the foramen of Winslow. From the fundus of the stomach it passes to the spleen, forming the anterior layer of the gastrosplenic omentum. It winds around the outer or costal surface, and the inner or renal surface of the spleen, and thence passes to the left kidney, forming the posterior layer of the lienorenal ligament. After covering the outer portion of the kidney, it is reflected to the abdominal wall which it follows to the median line.
Superficial to the peritoneum and between it and the structures which it covers is a layer of fibrous tissue which varies in thickness. The part which lines the muscles of the abdomen is called the transversalis fascia. It is thickest and most marked in the lower portion of the abdomen and accompanies the femoral vessels down the thigh.
In certain locations there is more or less fatty tissue between the transversalis fascia and the peritoneum, and sometimes it is impossible to differentiate them. They blend in the region of the kidneys, the mesenteries, inguinal regions, etc. In the femoral canal the transversalis fascia is continuous with the sheath of the vessels and the subperitoneal fat with the septum crurale. The protrusion of this subperitoneal fat in the median line usually above the umbilicus forms the fatty herniae alluded to on page 371.